Check if variable exist in laravel's blade directive

问题

I'm trying to create blade directive which echo variable (if variable defined) or echo "no data" if variable undefined.

This is my code in AppServiceProvider.php:

<?php

namespace App\Providers;

use Blade;
use Illuminate\Support\ServiceProvider;


class AppServiceProvider extends ServiceProvider
{
    /**
     * Bootstrap any application services.
     *
     * @return void
     */
    public function boot()
    {
        Blade::directive('p', function($ex) {
            error_log(print_r($ex,true));
            return '<?php $defined_vars = get_defined_vars(); if(array_key_exists(\''. $ex .'\', $defined_vars) ): echo ' . $ex . ' ; else: echo \'no data\'; endif;?>';
        });
    }

    /**
     * Register any application services.
     *
     * @return void
     */
    public function register()
    {
        //
    }
}

Here is my index.blade.php:

<p class="lead">@p($myvar)</p>

But my directive "p" gives "no data" if variable defined. If I use isset error occurres: Cannot use isset() on the result of an expression (you can use "null !== expression" instead)

How could I check inside directives if variable defined?

回答1:

Blade has a directive to check if a variable is set:

@isset($var)

@endisset

回答2:

For Laravel 5.7 onwards use.

{{ $checkvariable ?? 'not-exist' }}

回答3:

You can use in Blade functionality for checking isset i.e

{{ $checkvariable or 'not-exist' }}

https://laravel.com/docs/5.2/blade#displaying-data

回答4:

Try checking if the variable is empty:

@if(empty($myvar))
    <p>Data does not exist</p>
@else
    <p>Your data is here!</p>
@endif

Can also check this thread

回答5:

The best and cleanest way check if a variable exists in blade:

 {!! !empty($myvariable) ? $myvariable : 'variable does not exist' !!}

回答6:

For Laravel version >=5.7

{{ $value ?? '' }}

For Laravel version <5.7

{{ $value or '' }}

回答7:

You can use the @isset blade directive to check whether the variable is set or not. Alternatively, if you have the default value for that variable you can directly use it as {{ $vatiable ?? 'default_value' }}. The ?? way is available in Laravel v5.7 onwards.

If you want to check for multiple variables at once, you can do it by applying AND operation to expression as @if(isset($var_one) && isset($var_two)).

There are also other ways (lengthy) using @if directive as @if(isset($variable)) but it's not recommended.

Some developer uses @ symbol for error control in a similar situation. The at-sign (@) is used as error control operator in PHP. When an expression is prepended with the @ sign, error messages that might be generated by that expression will be ignored. If the track_errors feature is enabled, an error message generated by the expression and it will be saved in the variable $php_errormsg. This variable will be overwritten on each error. The use of @ is very bad programming practice as it does not make the error disappear, it just hides them, and it makes debugging a lot worse since we can’t see what’s actually wrong with our code.

回答8:

What are you trying to pass to your custom directive? If it's just a string/int the following should work.

Blade::directive('p', function($expression){
    $output = $expression ? $expression : 'nodata';
    return "<?php echo {$output}; ?>";
});

In Blade Template

@p('Foo')

回答9:

The @empty directive might be useful:

@empty($var)
   $var is unset or false-y
@endempty

回答10:

You can do it in few different ways.

Sample-1:

@if( !empty($data['var']))
   {{ $data['var'] }} 
@endif

Sample-2:

{{ $data['var'] or 'no data found' }}

Sample-3: Using ternary operator

<a href="" class="{{ ( ! empty($data['var'] ? $data['var'] : 'no data found') }}">

回答11:

If you trying check a bool variable you can use @unless

<input type="text" class="@unless ($variable) d-none @endunless" >

回答12:

For the last version of Larvael make the variable optional in the blade template. Replace $myvar with {{ $myvar }} with {{ $myvar?? '' }}

回答13:

To check if variable exist in Laravel blade directive, do this:

Blade::directive('datetime', function ($value) {
    
    return "<?php echo isset($value) ? ($value)->format('d/m/Y H:i:s') : null; ?>";
    
});

来源：https://stackoverflow.com/questions/37425978/check-if-variable-exist-in-laravels-blade-directive

标签

php

laravel

undefined

laravel-5.2

directive